The present invention relates to improvements in the coating of glass sheets or other substrates with thin films of a selected coating material and more particularly to the coating of such substrates by the cathode sputtering process.
The process of sputter-coating involves ion bombarding a target of the coating material in an ionized gas atmosphere in a chamber in which a controlled vacuum is maintained to cause atomic particles of coating material to be dislodged and deposited on the substrates to be coated. One type of apparatus employed for carrying out the process embodies a plurality of aligned, independently controlled contiguous chambers including an entry chamber, a coating chamber and an exit chamber, sputter-coating means in the form of a substantially rectangular cathode mounted horizontally in the upper portion of the coating chamber and having a sheet or layer of a selected coating material carried by the bottom surface thereof, and conveyor means for moving the substrates (glass sheets) in a horizontally disposed position through the successive chambers and beneath the sputter-coating means such that a continuous film of the selected coating material will be deposited on the upper surfaces of the substrates.
In such process, the thin films deposited on the substrates are usually of a metal such as, for example, nickel, gold, chromium, copper, molybdenum or titanium, or alloys of these metals. Typical sputtering conditions are 5,000 volts potential on the target (coating material) and a resulting current density of 0.5 to 1.0 ma/cm.sup.2 for a time period of 0.2 to several minutes depending on the thickness of coating desired. It will be appreciated that this potential on the target in the ionized gas atmosphere of the coating chamber will generate a very high temperature which tends to heat the metal cathode to an undesirable degree.
In order to maintain accaptable working conditions, it is essential that the cathodes be maintained at as low a temperature as possible and to accomplish this it has been heretofore proposed to provide them with means for cooling the same during the coating operation. However, the cooling procedures heretofore utilized have not proven entirely satisfactory in meeting the requirements continuous commercial operation. Further, the mounting means previously employed for supporting the cathodes in operative position have not been of such character as to permit ready removal and replacement of the cathodes in the coating apparatus.
This invention, therefore, contemplates an improved cathode of novel design which provides a more effective and uniform cooling of the cathode and, in consequence, a more rapid and efficient dissipation of the heat generated during the sputtering process.
Another object of the invention is to provide such a cathode of simplified yet durable and sturdy construction embodying a minimum number of parts and having means for easily and quickly removing and subsequently replacing the same when it becomes necessary to change or replenish the target material.